There are several Non-Governmental Organizations supporting their claim, and they work actively to prevent any further pollution.

actively 是形容词 active 的副词形式，active 意思是"积极的、活跃的"，加上 -ly 后缀构成副词，表示"积极地、活跃地"。 在这里 actively 修饰动词 work，表示"以积极的方式工作"。